We are studying genetic mechanisms that control the differentiation of the central nervous system. Our approach to this problem is to study two types of proteins in the brain that change their molecular forms during development. The first type is characterized by L-glycerol-3- phosphate dehydrogenase which possesses a molecular form in embryonic tissues differing from that in adult tissues. The embryonic and adult forms of L-glycerol-3-P dehydrogenase will be purified and compared; genetic variants of the adult enzyme in inbred strains of mice will be characterized so that the cellular mechanism controlling the expression of these two forms can be elucidated. The second type of protein being studied is characteristic of those proteins considered to be marker enzymes for the brain, choline acetyl transferase, acetylcholine esterase, and catechol-O methyl transferase. The expression of these marker enzymes and L-glycerol-3-P dehydrogenase are being compared in cell cultures derived from testicular teratomas and in embryonic and fetal tissues (6 to 16 days gestation) with the objective of finding correlatives in the expression of the cell-specific marker enzyme and the ability to express the developmentally dependent molecular form of L-glycerol-3-P dehydrogenase.